Tania A. Desrosiers, Ph.D., from the University of North Carolina at Chapel Hill, and colleagues analyzed data from the National Birth Defects Prevention Study. This included 1,740 mothers of infants, stillbirths, and terminations with anencephaly or spina bifida (cases) and 9,545 mothers of live born infants without a birth defect (controls), conceived between 1998 and 2011. A food frequency questionnaire estimated carbohydrate and folic acid intake before conception.

The researchers found that women with restricted carbohydrate intake had a mean dietary intake of folic acid that was less than half that of other women (P < 0.01). Women with restricted carbohydrate intake were slightly more likely to have an infant with a neural tube defect (adjusted odds ratio, 1.30).

"More research is needed to understand the pathways by which restricted carbohydrate intake might increase the risk of neural tube defects," the authors write.